HII regions slides

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Thermalization of energies and ionizationbalanceTo a good approx. the nebula contains only neutral H, protons (p), and electrons(e )The energy of the free electrons can be “anything” above 13.6 eVThe total energy available for photoionization depends on the total number ofphotons.This is a function of the effective temperature (T eff ) of the ionizing starThe energy is spread out (shared) between all the particles (by collisions)and acquires a single ‘kinetic temperature’ for all 3 types of particle.We say the plasma becomes ‘thermalized’.The distribution of velocities within the gas can now be described by a‘Maxwellian distribution’
AtomsThe Maxwellian DistributionVelocity
Page 1: Today:Recap on 1 st lecture:- Basic
Page 6 and 7: Distance = 450 pcDiameter ~ 1° (si
Page 8 and 9: Dark CloudsBok globules• relative
Page 12 and 13: ISM: average properties• Mean den
Page 14: A global view
Page 18 and 19: Cold, neutral medium (CNM)• domin
Page 20 and 21: www.milkywayproject.org
Page 22 and 23: Lagoon nebula
Page 25 and 26: PhotoionisationPhotoionisation: the
Page 27 and 28: Photoionisation: the removal of ele
Page 29 and 30: Balmer seriesLyman series(UV)Recomb
Page 31: Optical SpectrumPlanetary Nebula: N
Page 35: cross sectionse nucleuselectric fie
Page 39 and 40: For a typical O-star (e.g. the O6V
Page 42 and 43: M43Real examples1. no. of ionising
Page 44 and 45: However, Q per ionization is: (3/2)
Page 46 and 47: excitation/de-excitation of bound e
Page 48 and 49: Collisionally excited lines (CELs)B
Page 50 and 51: O +CELs (forbidden lines) are writt
Page 52 and 53: compare energy level diagrams1S 05.
Page 54 and 55: Forbidden line coolingtransition ra
Page 56 and 57: www.jodcast.netTopical podcast with
Page 59: DensitiesObservations n e ~ 100 cm
Page 62 and 63: Fraction of O2+ ions able to emit 4
Page 64 and 65: End of last lecture
Page 66 and 67: Today:HII regions: Practical method
Page 68 and 69: compare energy level diagrams1S 05.
Page 70 and 71: DensitiesObservations n e ~ 100 cm
Page 72 and 73: Practical methods and examples
Page 74 and 75: eal example
Page 76 and 77: • End of stellar existence for lo
Page 78 and 79: Optical Recombination Lines• ORLs
Page 80 and 81: Possible solutions?• Possibility
Page 82 and 83:
Any other ideas?• Possibility 3:
Page 84 and 85:
Knots: Abell 30• Results of empir
Page 86:
Conclusions• Cold H-deficient kno
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